Managed Extensibility Framework (MEF) is a built-in set of elements that allows you to “export” and “import” objects across projects which allows you not to rely on hard dependencies.
The Managed Extensibility Framework or MEF is a library for creating lightweight, extensible applications. It allows application developers to discover and use extensions with no configuration required. It also lets extension developers easily encapsulate code and avoid fragile hard dependencies. MEF not only allows extensions to be reused within applications, but across applications as well.